Results 1 - 10 of 1932
Results 1 - 10 of 1932. Search took: 0.028 seconds
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[en] The information theoretic measure of mutual interdependence between two sets of events, available when a probability distribution is given on their set-product, has been employed for a model independent analysis of the seismic data on the Calabria and Sicily regions over a twenty years period (1950-1970). Some preliminary results of this analysis are reported, showing which time ordered correlations between the seismic activity in different subregions can be evidenced from the data
[en] We consider the diffraction of Love waves by two parallel perfectly weak half planes in a layer overlying a half space. The problem is formulated in terms of the Wiener-Hopf equations in the transformed plane. The transmitted waves are then calculated using the Wiener-Hopf procedure and inverse transforms. (author)
[en] Analysis of published data on the fundamental parameters of actual accelerograms of strong earthquakes having peak ground acceleration A_m_a_x, predominant period T_p_r, and duration τ_0_._5 at 0.5A_m_a_x determined that, for earthquakes of intensity greater than 6.5 – 7.0, the relationship between these quantities is sufficiently well described by the parameters B = ATτ and C = AτT"−"1"."3"3"8, the former of which depends little on earthquake intensity I and is almost completely determined by the earthquake magnitude, while the latter, on the contrary, weakly depends on magnitude and is determined principally by the quantity I. Methods are proposed for using the parameters B and C to improve the reliability of determining parameters of accelerograms used to calculate the seismic resistance of hydraulic engineering facilities.
[en] The tsunami which occurred on December 28, 1908, in the Straits of Messina is examined. A wide set of data coming from a number of sources was collected and reviewed in order to get a picture as clear as possible of the generation and evolution of the event. The tsunami magnitude is estimated according to the Murty-Loomis scale, based upon the evaluation of the initial wave disturbance energy
[en] A study has been conducted to image seismic scatterers beneath the Gauribidanur (GBA) array in the Precambrian shield of south India. Short period digital data from teleseisms and regional events recorded over the 20 station L shaped array was used to image seismic scatterers beneath the array employing semblance technique. The results indicate a zone of dominant scattering encompassing the crust in a region west of GBA. The inferred zone of scattering coincides with a large N-S elongated granitic intrusion believed to be Precambrian suture zone between the East and West Dharwar craton. (author). 16 refs, 7 figs, 1 tab
[en] We introduce an approach to estimate the ratio between P- and S-wave velocities, v p/v s, in the scope of elastic full waveform inversion (FWI). Elastic FWI is generally implemented with local optimization methods relying on initial estimates of the long wavelengths of P- and S-wave models. However, successful inversions can be hindered if an accurate enough relation between v p and v s velocities is not used as a constraint. This relation can be estimated from empirical relations. Herein, we introduce an alternative approach based upon a semi-global inversion scheme. We observe that for a large number of cases, and particularly in the context of FWI, v p/v s can be represented on a sparse basis. This sparse basis has a much smaller dimension than that of the typical model space in elastic FWI. This creates the possibility of using global optimization methods. The optimal estimate of v p/v s is obtained with quantum particle swarm optimization (QPSO). This method probes a population of possible models. The assessment of each model of v p/v s in the population is obtained with nested local iterations updating for v p only. Conventional elastic FWI is then carried out for jointly estimating high-resolution models of v p and v s. We demonstrate with synthetic examples that the estimates of v p are relatively robust to errors in the estimated v p/v s, and that effectively a sparse representation of the model of v p/v s is feasible for the reconstruction of a model of v s. We also demonstrate that the proposed approach performs better than constraining elastic FWI with an empirical relation between v p and v s, leading to improved estimates of models of v p and v s from seismic data. (paper)
[en] Seismic waves propagating in a fractured geological medium are numerically simulated. Their dynamic behavior is described using a linear elastic model with an explicit description of all crack boundaries (a contact discontinuity problem is solved). An algorithm for seismic imaging of the fractured medium is proposed. A distinctive feature of this approach is the use of an initially fractured background model. The forward and adjoint wave fields are numerically computed by applying the grid-characteristic method on hexahedral meshes.